Mahan first rose to national prominence as director of the Union Grove High School band from 1936 to 1941. During this time he did special study at the Chicago Conservatory and received his B.S. degree in music from Texas Wesleyan College. After a period of teaching in Borger and Spring Hill, he enlisted in the Air Force and spent considerable time abroad, primarily in Japan, while director of the 361st AAF Band.
He was the director of bands at Texarkana, Texas, High School from 1946 to 1952. During this time he received his M.E. in Music Education at SMU in 1950. His thesis was a historical study of the Texas Music Educators Association from 1952 until 1956. 1961 he rose to the chairmanship of the music department at what is now UT Arlington. He has served many capacities in the TMEA, from band organizer to its President in 1949.